USE OF PUSH-PULL CANNULA TO ESTIMATE DYNAMICS OF ACETYLCHOLINE AND CATECHOLAMINES WITHIN VARIOUS BRAIN AREAS

The dynamics of cerebral neurotransmitters and thus the activity of the corresponding neurons as well as the changes caused by drugs can be indirectly measured by several methods. These methods are based on the use of labeled precursors, the measurement of the levels of transmitter metabolites or the determination of the concentration of the transmitters following compounds which interfere with their formation (e.g., .alpha.-methyl-p-tyrosine) or breakdown (e.g., monoamine oxidase inhibitors). The disadvantages of these methods in studying the effect of drugs imply the use of at least a 2nd compound which often possesses unspecific actions. Metabolic shifts of changes in the steady-state of the neurotransmitters cannot be excluded. Feedback mechanisms may rapidly mask the effect of drugs. Rapid, post-mortem alterations in the transmitter concentration or changes in the clearance of the metabolites may occur. The dissection of various brain regions is often an inaccurate, time-consuming procedure. Using specific and sensitive radio-enzymatic methods, the dopamine (DA), noradrenaline [norepindphrine] (NA) and acetylcholine (ACh) released were measured in cerebral areas of the awake, gallamine-immobilized or unrestrained cats with acutely or chronically implanted push-pull cannula. Some of the results obtained under various conditions are reviewed and the suitability of thia approach is discussed.